Piezometric thermionic tube



un 28, 1949. J. RmsmN 2,474,280

PIEZOMETRIC. THERE/[IONIC TUBE Filed April g2, 1946 2 Sheets-Sheet 1 FIG.3. 3M 1 JEROME ROTHSTEIN June 28, 1949; ROTHS' EIN 2,474,280

PIEZOMETRIC THERMIONIC TUBE Filed April 22, 1946 '2 Sheets-Sheet 2 FIG. 4

gvwwvtow JEROME RQTHSTEIN Patented June 28, 1949 PIEZOMETRIC THERMIONIC TUBE Jerome Rothstein, Belmar, N. J.

Application April 22, 1946, Serial No. 663,855

14 Claims. (Cl. 250-275) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to piezometric thermionic vacuum tubes, the outer envelope of which is provided with a diaphragm responsive to external pressure, the diaphragm being connected to one of the electrodes of the tube for varying the transconductance or amplification factor of the tube in response to the variation of the external pressure.

The piezometric tubes of this type are well known in the art. An example of such tubes is disclosed in the patent to Osborne, 1,548,095. Further modifications of such tubes are also disclosed in my U. S. Patent 2,389,935. In the tubes of this type a diaphragm is exposed to a variable gaseous or mechanical pressure, which results in such flexing of the diaphragm as to displace the plate or the grid of triode with respect to the remaining electrodes of the tube with the concomitant increase or decrease in the space current of the tube.

The structure disclosed in this application differs from the prior art in the introduction of an additional mechanical element for decreasing the sensitivity of the diaphragm in responsefto increase in pressure beyond a value which produces a preselected strain in the mechanical element, thus increasing the useful pressure range of the piezometric tube.

With some modifications of the parameters of the same structure it may be used alsofor accentuating the sensitivity of the piezometric tube in the desired portion ofthe total pressure rangeof the tube so that the structure not only increases the useful pressure range but may be used also to produce a non-uniform, preselected sensitivity characteristic.

It is therefore an object of this invention to provide a piezometric tube provided with a pressure-responsive diaphragm mechanically connected to one of the electrodes of the tube, and an additional mechanical element which becomes mechanically coupled to the diaphragm in a progressive manner for progressively lowering the elasticity or displacement of the diaphragm with the progressively increasing pressure upon the latter.

Still another object of this invention is to provide a piezometric tube with a diaphragm responsive to external pressure, this diaphragm being connected to one of the electrodes of the tube for varying the transconductance or the amplification factor of this tube in response to the variation in the external pressure, and additional instrumentalities connected to the diaphragm for varying the sensitivity of the diaphragm to the pressure exerted on the diaphragm, said instrumentalities being externally adjustable so that the tube in effect is provided with an external adjustment of its amplification factor and adjustment of the sensitivity over the pressure range so that it is more sensitive in one portion of the range than in the remaining portion.

To accomplish the foregoing and more specific objects which will hereinafter appear more clearly upon the description of the drawings in which:

Figure 1 is a cut-away isometric view of a three-element piezometric tube;

Figure 2 is a sectional view of a portion of a piezometric tube similar to thatdisclosed in Figure 1 but with difierent internal connections;

Figures 3 and 4 illustrate vertical sectional views of three-element thermionic tubes in which the mechanical sensitivity-controlling members are mounted on the outer surface of the diaphragm;

Figures 5 and 6 illustrate plan views of the auxiliary mechanical elements which may be coupled to the external surface of the diaphragm, as illustrated in Figures 3 and 4;

Figure 7 illustrates an additional modification of the pressure-responsive structure in which the pressure transmitting rod is provided with a lateral support, and the tension, as well as spacing of the pressure-responsive diaphragm from the bafile are made adjustable.

Referring to Fig. '1, it discloses a vacuum triode in a glass envelope Ill, with a conventional glass press l2 which supports five metallic rods ll, l3, l4, I5, and I 6 used for completing the electrical circuits as well as for mechanically supporting the indirectly heated cathode l1, and a grid element [8. The upper end of envelope I0 forms a glass seal 20 with a Kovar ring l9, and the ring is brazed at a junction 2| to a baflle support 22. The bafiie support includes an outer ring portion 33 and an integral curved washer portion 25, the upper surface of this washer being curved so as to form a funnel-like surface, as illustrated in the figure. A metallic diaphragm 23 fits over the washer portion of the baille, the diaphragm being brazed at a junction 24 to the ring portion 33 of the baflle. Thus, there is a gas-tight joint between the diaphragm and the baflle support. the baffle support and the Kovar ring l9, and

ring I!) and the glass envelope Ill. The tube is degassed in the, usual manner, and is provided with a base 26 and prongs 21-23 for completing the cathode and the grid circuits. Plate 30 is welded to a rod 32 and the rod is also welded to diaphragm 23. The plate circuit is completed through a conductor 34 connected to a binding post 36.

Examination of the structure illustrated inj Fig. 1 reveals the fact that the cathode and the grid remain in fixed mechanical position with respect to each other since they are supported by the fixed metallic rods l3-l6 embedded in the glass press. Plate 30 of the triode, however, is connected to the diaphragm 23, and, therefore, the position of this plate with respect to the grid will be a function of the position of diaphragm 23 with respect to the glass envelope In or baffle 25. Thus it may be stated that if bafile 25 is removed from the construction illustrated in Fig. 1, the structure would then represent a well known, conventional piezometric tube in which flexing of the diaphragm varies the transconductance or amplification factor of the tube. The modification resides in the introduction of bafile 25, the upper surface of this baflle, i. e.. the surface adjacent to diaphragm 23; being curved so as to vary the sensitivity of the piezometric tube in any desired manner, depending upon the contour given to this surface of the baflle.- Its function is to give a desired, preselected dependence of plate displacement with the increase in pressure applied to diaphragm 23.

The elastic displacement of a diaphragm without any baflie is defined by a formula:

=%: or the ratio of radical coordinate Ar of a point on the disc to the radius 1'. Examination of this formula reveals the fact that one or more of the quantities r, t, G, E and K could be made to vary in a suitable manner to secure the desired functional dependence. G and E being characteristic of the disc material, could only be changed with great difliculty, if at all, since this would presumably involve the use of more than one material. This is undesirable because the use of diflerent materials would give rise to disturbances arising from their difi'erent coeflicients of expansion. K, between the two extremes of a free and clamped disc, varies in value over a range of approximately 5 to 1 and would, in application, probably be restricted to a small fraction of even this small range of variation. Accordingly, it alone is insufiicient to control the deflection characteristics over a very wide range. The functional dependence of X on 1' and it, however, is very marked, being 4th power of 1' and inverse 3rd power of it. Thus it is apparent from the examination of the above formula that if onewishes to have an extremely sensitive diaphragm responding to very minute diflerences in pressure, one would make it very thin and having a large diameter. However, since the variation in the spacing between the plate, the grid and the cathode can hardly be varied effectively from the electrical point of view, over a large distance, it is obvious that any increase in the sensitivity of diaphragm 23 could be generally accomplished only at the expense of the measurable pressure range. When one is confronted with the requirement which calls for a very wide range as well as exceptionally high sensitivity in the low pressure range, it is obvious that these two mutually opposing requirements can not be satisfied by resorting to the use of a conventional diaphragm. The invention offers an efiective and simple solution of this problem. The baiile is given such curvature that in the low pressure range diaphragm 23 having small thickness, t, and large radius, 1', produces sufiiciently large displacements to produce the desired large changes in the transconductance or amplification factor of the tube. However, as the external pressure exerted on the diaphragm 23 increases, its lower surface begins to engage the curved surface of baffle 25. Since bafile 25 represents, for all practical purposes, a rigid supporting surface, engaging of this bafile by diaphragm 23 is equivalent to the reduction in the radius r of the diaphragm. Equation 1 states that the displacement of the diaphragm is proportional to the 4th power of the radius of the diaphragm, and as a consequence, there will be a very rapid decrease in the sensitivity of the diaphragm, and in the rate of change of the amplification factor of the tube, as the pressure exerted on the diaphragm increases to such an extent that larger and larger areas of the diaphragm encounter rigid support provided by the baffle.

With proper shaping of the bailie very wide pressure range can be obtained, and the overall sensitivity controlled so as to obtain, if so desired, an approximately logarithmic relationship between pressure, P, and plate current Ip. The disc constant K will also vary to some extent with the variation of 1 but its quantitive effect will be inegligible compared to the 4th power variation of the diaphragm radius 1'. Because of the complexity of exact mathematical analysis or deviation of the shape of the baflie curve, it is simpler to obtain the sought result by resorting to mathematical approximations and cutand-try methods.

Fig. 2 illustrates a modification of Fi 1; diaphragm 23 is now connected to an adjustable grid 200 so that in Fig. 2 it is the cathode 202 and plate 204 that are supported by the glass press 12 (not illustrated in Fig. 2) while grid 200 is moved either (away or toward plate 204 in response to the variation in pressure exerted on diaphragm 23.

Figs. 3 and 4 illustrate an additional modification of the principle exemplified by Figs. 1 and 2; .in Figs. 3 and 4 the sensitivity of diaphragm 400 is varied either by one or two external spring members 402 and 404, attached to an electrode supporting rod 406, which protrudes through diaphragm 400. It is to be understood that there is a gas-tight joint at this joint. The-external spring members 402 and 404 may be either of circular shape or of bar or star type,.as illustrated in Figs. 5 and 6. When these members have circular surfaces and these surfaces given a curvature so that it begins to engage the deflecting diaphragm '400 progressively upon the increase in pressure or only after a predetermined pressure has been exerted on the latter, the effect of such member 402 on diaphragm 400 would be also. equivalent to varying the radius of the diaphragm except that while in Figs. 1 and 2, the variation of the radius is proceeding inwardly, or toward the center of the center of the diaphragm, from the external rim of the diaphragm, in Figs. 3 and 4 this variation in radius is proceeding outwardly fromthe center of the diaphragm so that at some predetermined pressure the diaphragm begins to act as a flexible washer with the central portion of the washer being inflexible due to the presence of spring 602, and only the remaining portion of the diaphragm responding to the increase in the external pressure. In Figs. 3 and 4, two spring members 302 and 40 i are illustrated. It is obvious that the number of these members, when they are in a form of a sector spring 600, or disks 500 and 502, may be either decreased to one or increased to a greater number than two, if so desired, which may be the case when springs M2 and Mid are made very flexible so that they offer only a very limited resistance to the deflection of the diaphragm. When member 302 is of the circular bowl type, it is obvious that its shape makes it so rigid that the use of any additional similar members, such as 4174, becomes useless, and in this arrangement the sensitivity must be controlled by properly selecting the radius of the bowlshaped springs 402 and W5. The advantage of the arrangement disclosed in Figs. 3 and 4 resides in the fact that the deflection controlling bafile or the deflection controlling springs are mounted directly on the outer surface of the diaphragm 40B, and are held engaged with diaphragm 50!] by a nut 308. Therefore, the sensitivity and the range of the pressure measuring tube may be altered at will by taking 01? the elements 602 and cut, which makes the tube rnost sensitive to pressure, or by clamping to diaphragm 600 a circular baiile or a spring or a plurality of springs which decrease the sensitivity of the tube to any desired extent. Accordingly, Figs. 3 and 4 disclose a somewhat more versatile structure than the one disclosed in Figs. 1 and 2. The diaphragm may be connected either to the grid or to the plate, the former connection being used in Fig. 3, while the latter in Fig. 4.

The sector-shaped spring Gill! illustrated in Fig. 6 may be either a curved or a flat spring. It is also possible to use flat discs 5% and 502, illustrated in Fig. 5, which may be considered as one specific case of the springs 582, see and 600 in which the radius of curvature and the number of radial projections of the spring has been increased to infinity.

Figure '7 discloses an additional modification of Fig. 1. In both figures the bafiie represents an element mounted internally in the degassed space of the vessel. As in the case of Fig. 1, a pressureresponsive diaphragm 100 is connected to a rod 102 which varies the spacing between the grid and the plate. The ring portion of the 'baflle support is provided with threads 1M and bellows I06. The bellows are connected between the rim of the ring and the diaphragm thus completing the gas-tight connection between the diaphragm and the battle. A threaded circular member or nut 108 is in threaded engagement with thread 104. Nut "18 is also provided with a ring "15 which engages, with its lower end, diaphragm 100 along the circumference adjacent to the edge of the diaphragm so that tightening of member 108 lowers diaphragm 100 and brings it closer to 6 the bafile. If tightening of member 808 is continued after diaphragm 10!! touches baffle H0 at 1 I 4, there will be flexing of the diaphragm around the surface of revolution He because of the fact that baflle H0 is provided with a recessed curved surface N2, the diaphragm extending over this surface. Therefore continued tightening of nut H18 will flex the diaphragm around point lid on the upper surface of the baffle and will simultaneously increase the tension exerted by the nut on the diaphragm. This will decrease the sensitivity of the diaphragm by decreasing its radius as well as by increasing its stiffness because of 7 tion in said pressure, and a curved baffle mounted the additional tension imposed upon it by ring 135.

While the invention has been disclosed in connection with the mechanical arrangements which are particularly suitable for measuring atmospheric, or any other gas pressures, since there are no external connections illustrated between the diaphragm and any other mechanism, it is to be understood that the devices may be used for other purposes and, in general, measurement of rapidly or slowly varying pressures may be transmitted to the diaphragm by any mechanical means rather than through the pressure of gases. Therefore, the term pressure as used in this specification includes any physical quantity capable of causing displacement of the diaphragm.

While the invention has been described with reference to several particular embodiments, it will be understood that various modifications of the apparatus shown may be made within the scope of the following claims.

I claim:

1. A piezometric thermionic tube comprising a degassed vessel, a cathode, an anode electrode, and at least one grid electrode, a diaphragm forming a portion of the wall of said vessel, said diaphragm being responsive to an external pressure, a connection between said diaphragm and one of said electrodes for varying the amplification factor of said tube in response to the variation in said pressure, and a mechanical member mechanically coupled to said diaphragm and having a shape permitting progressive engagement between said member and said diaphragm with an increase in said pressure for varying the degree of flexing of said diaphragm with the increments of said pressure along the operating range of said tube thereby increasing said range.

2. A piezometri'c thermionic tube comprising a degassed vessel, a cathode electrode, an anode electrode, and at least one grid electrode, a diaphragm forming a portion of the wall of said said pressure said mechanical member increasing the pressure'range of said tube.

3. A piezometric thermionic tube comprising a degassed vessel, a cathode, an anode electrode. and at least one grid electrode, a diaphragm forming a portion of the wall of said vessel, said diaphragm being responsive to an external pressure, a connection between said diaphragm and one of said electrodes for varying the amplification factor of said tube in response to the varia- 7 within the envelope of said tube adjacent to the inner surface of'said diaphragm for progressively decreasing the strain produced in said diaphragm with the increase in said pressure.

4. A piezometric thermionic tube as defined in claim 3 in which said baflle is provided with a central opening for said connection, and the curvature of said baiile is such as to decrease progressively the effective radius of said diaphragm by offering progressively increasing supporting annulus areas with the increase in said pressure.

5. A' piezometric thermionic tube as defined in claim 3 which also includes instrumentalities for externally adjusting the spacing between said diaphragm and said. mechanical member for adjusting the sensitivity of said tube to said pressure.

6. A piezometric thermionic tube comprising a degassed vessel, a cathode, an anode electrode, and at least one grid electrode, a diaphragm forming a portion of the wall of said vessel, said diaphragm being responsive to an external pressure, a rod rigidly connected to the center of said diaphragm and one of said electrodes for varying the amplification factor of said tube in response to the variation of said pressure, a baflie mounted adjacent to the inner surface of said diaphragm for varying the degree of flexing of said diaphragm with the increments of pressure along the operating range of said tube, and a central opening in said baille, said rod passing through said opening.

7. A piezometric thermionic tube comprising a degassed vessel, a cathode, an anode electrode, and at least one grid electrode, a diaphragm forming a portion of the wall of said vessel, said diaphragm being responsive to external pressure, a connection between said diaphragm and one of said electrodes for varying the amplification factor of said tube in response to the variation in said pressure, and a mechanical member mounted on the external surface of said diaphragm for progressively decreasing the strain in said diaphragm with the increase in said pressure.

8. A piezometric thermionic tube as defined in claim 7 in which said mechanical member is a curved, rigid member, the convex surface of said member facing the outer surface of said diaphragm.

9. A piezometric thermionic tube as defined in claim 7 in which said mechanical member is a star-shaped curved spring, the convex surface of said spring facing the outer surface of said diaphragm.

10. A piezometric thermionic tube as defined in claim 7 in which said connection between said diaphragm and one of said electrodes comprises a rod protruding through said diaphragm, and means for demountably attaching said mechanical member to the protruding portion of said rod. 11. A piezometric thermionic tube as defined in claim 7 in which said mechanical member is a plurality of fiat discs of decreasing diameters, the disc adjacent tothe diaphragm having the reatest diameter and the disc farthest from the diaphragm having the smallest diameter.

12. A piezometric thermionic tube as definedin claim 7 in which said mechanical member comprises a plurality of curved, slotted spring members of progressively decreasing diameter, the spring member with the greatest diameter being adjacent to said diaphragm, said spring members being placed on said diaphragm with the convex surfaces facing the outer surface of said diaphragm.

13. A piezometric thermionic tube comprising, a degassed vessel, a cathode, an anode, and at least one grid electrode, an elastic first member forming a portion of the wall of said vessel, said first member being responsive to an external pressure, a connection between said first member and one of said electrodes for varying the amplification factor of said tube in response to the variation in said pressure, and a second mechanical member in contact with said first member, whereby a change in said external pressure moves said first member into a progressively larger engagement with said second member for varying the rate of change of displacement of said first member with the increments of pressure along the operating range of said tube.

14. A piezometric tube comprising a degassed vessel, a plurality or electrodes in said vessel, 9. pressure-responsive member forming a portion of the outer wall of said vessel, a connection between said member and one of said electrodes for varying the thermionic current in said tube in response to the variation in said pressure, and a mechanical member capable of engaging said pressure-responsive member only after a predetermined change in said pressure-for varying the sensitivity of said pressure-responsive member with the change in said pressure and for varying the pressure-response characteristic of said tube.

JEROME ROTHSTEIN.

REFERENCES CITED UNITED STATES PATENTS Name Date Sampson July 11, 1939 Number 

